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Dissociation constant

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Description of key information

Read-across from a similar substance shows the dissociation constant of 7.5.

Key value for chemical safety assessment

pKa at 20°C:

Additional information

In the preliminary test it was determined, that due to the low water solubility of 77PD, the dissociation constant cannot be performed according to the titration method. Thus a study performed with 44PD, a similar substance was used. The measured value and the QSAR demonstrate that both, the neutral and the mono-protonated form of the substance will be present at the environmental relevant pH of 7.

Due to the low water solubility also of 44PD, the titration had to be performed in a system containing about 30% methanol. Typically, the pKa in pure water would be expected higher, in the range of 7.5 to 8.